Duct Board, Premium HVAC duct material or health hazard?

Duct board is a pressed fiberglass sheet with a binder that is commonly used in heating and cooling systems. The sheets are typically available in three thicknesses (1", 1.5", or 2") with R-values of either 4, 6, or 8 and the sheets have dimensions of 4' x 8', 4' x 10', or 8' x 10'. These sheets are cut and formed into squares that are connected and provide a path for airflow in the heating and cooling system.

Advantages & Disadvantages

The advantages of using fiberglass ducts include energy efficiency due to their material, manner of construction, and manner of installation. The are fabricated with a system of grooved cuts and folding that provide an air tight seal which means the conditioned air can be better controlled and delivered to the desired area without leakage. The material is fiberglass and it is an insulator meaning the conditioned air maintains its temperature better than standard uninsulated metal ducts. These facts combine so that, in many cases, it is possible and advisable to install smaller heating and cooling equipment.

** HOT TIP** Remember that it is only through a load calculation that the required size of equipment can be determined.

Another advantage is the fact that the systems are normally much quieter than metal or flexible duct systems. Many metal duct systems (even those that are properly installed) have vibration noise as well as popping sounds from the metal expanding and contracting with the change in temperature. This common complaint is eliminated with properly installed fiberglass duct board systems. The systems also typically have less flow noise when properly sized.

The fact that the ducts are lighter and easier to hang than metal ducts is another advantage and they are easier to modify and assemble but that leads us to their biggest disadvantage. The tools to cut and fabricate the ducts are expensive.

Another main disadvantage is the fact that the materials are more expensive than a uninsulated metal duct but they are comparable to insulated metal systems.

Finally, these systems do not stand up to moisture and so they should not be installed in areas that are damp.

Common Internet Myths About Duct Board

If you do a routine search for these ducts, you will be overwhelmed and even scared by most of the claims concerning these ducts. The most common myth is that the fibers get loose over time and are spread throughout the home resulting in breathing problems for people. Scientific studies show that this is a myth and simple pictures of systems that have been in operation for years show how this is not true. If you look at a picture of most of these systems that have been in operation for awhile, you will see a buildup of dust similar to what you find in any duct system. Common sense tells us that, if dust will settle out of the air stream, then, fiberglass would as well.

Another myth is that these systems contribute to the growth of mold and bacteria in a duct system. For mold to occur, moisture is required and these systems should not be installed in such places as very damp crawlspaces etc. Also, most of the manufacturers provide a product with a coating that prevents mold growth.